In recent years, among mobile terminals such as cellular phones, electronic devices are increasingly provided with a touch sensor, such as a touch panel or touch switch, as a member for detecting an operation by the operator. Electronic devices provided with a touch sensor are in wide use apart from mobile terminals as well, in devices such as calculators or ticket vending machines, household appliances such as microwave ovens, televisions, or lighting appliances, industrial devices (factory automation equipment), and the like.
A variety of types of such touch sensors are known, including a resistive film type, a capacitive type, and an optical type. All of these types of touch sensors detect contact by the operator's finger, a stylus pen, or the like. Typically, an electronic device provided with a touch sensor displays an image (hereinafter referred to as an “object”) of an operation key, a button, or the like on the display screen of a display unit provided on the rear face of the touch sensor. In such an electronic device, when the operator presses an object displayed on the display screen, the touch sensor is configured to detect contact at the position of the press.
A variety of touch sensors have been proposed (for example, see Patent Literature 1). Patent Literature 1 proposes an analog resistive film type touch panel that can be produced at a low cost and with a reduced size. The touch panel disclosed in Patent Literature 1 has two conducting films with a slight gap therebetween provided by a spacer. The touch panel is configured to read the position of contact at which the conducting films are pressed as a voltage at one conducting film based on the voltage gradient on the other conducting film.
Many electronic devices provided with the above-described touch sensor perform different, predetermined processing in accordance with the position of the contact detected by the touch sensor. In other words, in the touch sensor corresponding to the object region displayed on the display unit, different processing is often allocated to each object. For example, in such an electronic device, a menu screen is displayed when contact is detected on the touch sensor at a position corresponding to a menu button object, whereas the cursor is moved when contact is detected on the touch sensor at a position corresponding to an arrow key object. When, for example, the processing to be initiated is thus distinguished in accordance with input corresponding to a plurality of objects, the accuracy with which the position of contact is detected is important when the touch sensor detects the contact. Therefore, when detecting the position of contact with a touch sensor, a technique has been proposed to accurately detect the position of contact (for example, see Patent Literature 2).